The present invention relates generally to high performance servo valves and more particularly to a zero lap, high frequency response servo valve.
In the past, high performance servo valves were of conventional spool valve design but were manufactured using special tolerance, skill, and production techniques. In these servo valves, the valve body porting was accomplished by using a special spool bushing consisting of a plurality of separate segments which were precision controlled as to axial length and which were brazed together to form inlet, load and outlet ports. Spools were precision fitted into the spool bushings and then were uniquely matched thereto by machining the spool lands with special hydraulic gauging equipment to exactly match their corresponding ports so as to minimize the lap which is the length of the ports blocked position.
By utilizing precision manufacturing techniques, it is possible to minimize lap, but there will always be some under or over lap due to inherent tolerance variation in the spool valve design. The ideal high performance servo valve would be an easily manufactured valve having zero lap or minimum null shift, high frequency response, exact linearity and pressure gain, high spool driving forces, minimum resolution and hysteresis, high contamination tolerance, and long life with high reliability.